A nitrogen fertiliser already used quite widely in Germany could help UK growers in their quest to match that country’s generally higher oilseed rape yields.

Perlka, made of limestone, coal and atmospheric nitrogen, is a 20% N-50% calcium oxide product, the balance being mainly inert materials such as carbon and silica, says importer Paul Corfield of PP Products in Norwich.

Made in Germany, Perlka was widely used in the UK before World War II, says Mr Corfield. But with its N content relatively expensive compared with that from ammonium nitrate and urea, its use in the UK since its reintroduction in 1996 has been mainly in vegetable production.

However, the rising price of AN and urea has made Perlka, at £487/t, more competitive, especially when its other properties are taken into account, he says.

Its nitrogen is only slowly released, thus minimising leaching, and it has bio-control and soil conditioning effects.

“Oilseed rape growers in Germany know well the benefits and use 16,000-18,000t a year at rates of 200-250kg/ha at drilling.”

Trials by ADAS and Masstock are under way to see how useful that approach may be against diseases such as club-root and sclerotinia.

ADAS pathologist Peter Gladders, involved with a three-year HGCA project testing Perlka against club root, describes it as “promising”.

In one experiment on infected land in Shropshire it helped produce what appear to be satisfactory crops, he says. “The untreated area was pretty well wiped out. But it’s still early days, and we’re trying to define what cost-effective rates may be.”

On heavily infected soils, resistant varieties – the only one available being Mendel – may well still be necessary, Dr Gladders believes.

Masstock’s main interest in the product was sclerotinia-driven, says the firm’s Carl Flint. The aim is to examine what might be done to reduce soil sclerotia numbers and so ease spring pressure from the disease and save on flowering fungicides.

So a Berkshire trial is examining the impact of autumn and spring applications of 200kg/ha of Perlka alongside autumn treatments of Contans, an approved fungal parasite of sclerotinia.

Despite the N price movements Perlka fertiliser remains relatively expensive, notes Mr Flint. “So it needs to deliver a lot to be economically viable in winter rape.”

Andrew Rennie, parts of whose farm in Aberdeenshire have been affected by club root for some time, has tried Perlka for two seasons.

“We’re finding it gives much stronger plants with better root formation from the start,” he says.